A flatbed truck is supported by its four drive wheels, and is moving with an acceleration of 6.9 m/s2. For what value of the coefficient of static friction between the truck bed and a cabinet will the cabinet slip along the bed surface

The cabinet will slip along the bed surface for the values of coefficient of static friction lesser than 0.7

Explanation: Please see the attachments below

The coefficient of static friction is  

Explanation:

 From the question we are told that

          The acceleration is

The mathematical expression that show the relationship between frictional force and the sliding  force of the cabinet at the point just before sliding begins is

Now  

   Where m is the mass of the cabinet

                g is the acceleration due to gravity

                is the coefficient of static friction

And  

  Where a is the acceleration due to gravity

               Now substituting this into the equation

Substituting values where